Inline Sewage Pump

Inline Sewage Pump

What is an inline sewage pump?

An inline sewage pump is a type of centrifugal pump used for draining solid particles and long fibers. Inline sewage pump manufacturers also refer to it as a straight-line pump because its suction and discharge ports are oriented straight to the piping system. In other words, the centerline of the pump’s inlet and outlet is on the same level. It uses a unique impeller structure and mechanical seals that help to effectively contain fibers and solids as they are being transferred. The inline sewage pump features a vertical installation, single- stage and single-suction design. It also combines the characteristic of the basic water pump. The working operation of an inline sewage pump is based on the principle of gravity-fed sewage directly from the entry point. It has a relatively small size; hence it takes up less floor space compared to other types of sewage pumps. The pump inlet and outlet flanges are cast in a single body thereby making the pump easy to install and disassemble.

Configuration of an inline sewage pump

Figure: Configuration of an inline sewage pump

An inline sewage pump offers attractive performance metrics with a capacity of 3000 cubic meters per hour, a wide operating range of operating speeds (from 740 to 2900 RPM), and a maximum pressure head of 6 bars. It can handle medium temperatures of up 60 degrees centigrade. The inline sewage pump can perfectly cater to different applications, including industrial wastewater treatment, oily water, urban environment, construction, firefighting, pharmacy, dye, power plants, chemical industry, plating, paper making, washing of industrial mines, cooling of equipment, and many more. Inline sewage pumps are widely preferred because of their robust design, which is floor space-saving and easy to transport and mount. Inline sewage pumps can also handle fluids at high temperatures and pressure because the inline sewage pump manufacturers equip them with the ability to resist thermal expansion. An inline sewage pump requires less suction pressure because it is installed anywhere along the pipeline like a valve. The low suction pressure requirement allows the pumping medium to flow through the pump with ease.

Components of an inline sewage pump

Components of an inline sewage pump

Pump body or housing

The pump body or housing supports and protects most of the pump interval components, including the shaft, bearings, impeller, shaft sleeve, etc. The pump housing is usually sealed to retain pressure and protect against leakage. It houses vital parts of the pump. The pump housing also features the inlet and outlet flanges that guide the fluid into the pump at suction pressure and out of the pump at higher pressure.


The function of the motor is to spin the pump impeller or simply to run the pump. It works by converting electrical energy into mechanical energy. An electric motor can be either an AC motor or a DC motor. Ac motors work with alternating current, while Dc motors operate with direct current.


The is a rotary mechanical component supported by the bearing and carrying the impeller. Its function is to rotate the impeller to displace the fluid in the pump. The pump shaft, bearing, and impeller form the rotor assembly, which connects to the electric motor through a coupling. In an inline sewage pump, the motor shaft carries the pump impeller i.e., the shaft is closely coupled to the pump impeller.


The impeller moves fluid that comes in through the pump inlet and exits through the outlet. Inline sewage pump manufacturers can design impellers in either axial flow design, where the fluid flows axially to the shaft, or radial flow design, where fluid flows radially to the shaft. Radial flow impeller can have either an open or closed impeller design. Open impellers have only one shroud, and the vanes are exposed on one side. They are mainly used in single-stage, single-suction centrifugal pumps. A closed impeller has a cover on either side; the impeller vanes are sandwiched between the two shrouds. Closed impellers are mostly used in radial flow centrifugal pumps and can have a single or double suction configuration. An inline sewage pump employs an open impeller because it can efficiently handle large amounts of suspended bodies and fluids with high viscosity.

vShowing closed impellers: single and double suction configurations

Figure: Showing closed impellers: single and double suction configurations.


The bearings carry the rotor assembly and ensure that it aligns perfectly with the pump body. They carry the fully rotary load of the shaft during operation and minimize friction between the rotating shaft and the stator for smooth operation.

Mechanical seals

The mechanical seals serve to prevent fluid under pressure from leaking out of the pump. Mechanical seals also prevent the pump from drawing in the air under vacuum conditions.

Pump Inlet and outlet

The pump inlet connects with the waterline while the outlet connects to the household water distribution piping. The pumping medium enters the pump through the inlet section and discharges via the outlet section.

How does an inline sewage pump work?

The motor impeller is rotated through a directly coupled AC electric induction motor. The rotation of the impeller creates a vacuum inside the pump casing. As result, the atmospheric pressure outside the pump forces the liquid into the pump casing through the pump inlet. When the liquid strikes the blades of the impeller, it is rotated radially and axially outwards, due to the centrifugal force acting on the blades, until it passes through all of the impeller components. The impeller blades impart kinetic energy to the liquid and direct it toward the diffuser chamber at a very high speed. In the diffusing chamber, the speed of the water is gradually decreased leading to the conversion of the high-velocity energy into a high-pressure head. The diffuser then guides the water to the pump outlet and into the delivery pipe to be transferred to the required location.

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Figure: Working of an inline sewage pump

Types of inline sewage pump

Vertical inline sewage pump

A vertical inline sewage pump consists of a vertically oriented shaft that is close coupled to the pump head. It is the most common design of an inline sewage pump. Sometimes the pump can be long-coupled via the use of a spacer bracket acting as a support for the motor. The long-coupled design allows easier pump maintenance because the motor does not have to be removed during repair.

Showing a vertical inline sewage pump

Figure: Showing a vertical inline sewage pump.

Horizontal inline sewage pump

A horizontal centrifugal pump is characterized by a horizontally oriented shaft and impeller, typically between pump bearings. The motor is located on the same horizontal plane and adjacent to the pump

Inline sewage pump manufacturer

Figure: Showing a horizontal inline sewage pump.c

Applications of an inline sewage pump

Inline sewage pumps find a wide range of applications in different industries, such as urban wastewater treatment plants, construction, firefighting, pharmacy, industrial mines, paper making, etc. Typical uses include:

  • An inline sewage pump is used for transferring sewage in treatment plants
  • It is also used for pumping industrial wastewater.
  • Inline sewage pumps are also applied in the washing of industrial mines
  • It is also used for moving oily water.
  • It is also used in private homes and buildings that are not connected to municipal sewers due to the nature of the terrain.
  • It is used in chemical industries to transport viscous fluids.
  • It is also used in industrial recirculation.
  • It can also be used in fire control.
  • It is used for pumping any liquid containing suspended particles and fibers.

Advantages of inline sewage pump

  • An inline sewage pump has high reliability and efficiency
  • Inline sewage pumps are suitable for high pressure and temperature because they can resist thermal expansion.
  • Inline sewage pumps require small space for installation. The motor and service clearance is located above the pump casing, requiring less floor space for pump installation.
  • Inline sewage pumps do not require regular maintenance because they have few parts that experience wear.
  • Inline sewage pumps are easier to install and operate because they have a simplified construction. The close-coupled design does not require shaft alignment or additional bearing assembly.
  • Inline sewage pumps also have a low Net Positive Suction Head Requirement (NPSHR) and thus can easily move fluid through the pump.
  • An inline sewage pump produces less noise and vibration.
    The vertical shaft orientation is naturally balanced and gravitation forces do not oppose the shafts rotation direction.

Disadvantages of inline sewage pump

  • An inline sewage pump can be difficult to maintain because the motor and impeller must be disassembled from the volute to service the mechanical seals. This is particularly a major challenge for the pump with large motors, above 25 hp.
  • The inline sewage pump requires vertical clearance for installation and maintenance.
  • They have the risk of running backward especially when the pump is stopped without first closing the discharge line.
  • Air leakage can reduce the inline sewage pump capacity.
  • The weight of the pump falls below the volute, leading to a large stress concentration.

Troubleshooting inline sewage pump

The inline pump zero discharge after startup

  • The inline pump operation is reversed. Ensure that the direction of the motor rotation matches the direction indicated by the inline sewage pump manufacturer using the arrow in the nameplate. Reverse the motor polarities
  • There is air in the pump or suction pipework. Fill the pump or pipework with water to drive out the air from the pump system.
  • The impeller or check valve is clogged. Inspect and clean any blockage in the valves
  • The monomeric head is insufficient due to high friction losses that exceed the pump design. Increase the pump power. Make sure the pipes used in the piping network meet the recommended diameter by the inline sewage pump manufacturer.

Inlet pump experiencing excessive vibration

  • Some pump components are unbalanced. Inspect and rebalance parts if necessary.
  • The pump impeller is partially clogged. Inspect and clean the impeller.
  • The impeller is severely worn out or defective. Inspect and replace the impeller.
  • Some pump components are loosely held within the pump body. Tighten any loose parts to the torque level recommended by the inline sewage pump manufacturer.

The noise level is too high

  • There is air in the liquid. Ensure that the suction pipe is completely submerged to prevent the formation of vortexes on the surface of the liquid
  • Pump working in cavitation. Check that the suction line valves are fully open.
  • The pump is working outside the duty range. Ensure the correct duty range according to the inline sewage pump manufacturer’s manual.

The Inlet pump driver overloaded

  • The Pump speed is too high. Reduce the pump speed.
  • Faulty pump motor. Inspect the motor for defects and repair or replace it if necessary.
  • Some pump parts are subject to extreme mechanical friction. Inspect the pump assembly for any obstruction or deflection and correct it.


An inline sewage pump also called a straight-line sewage pump, is a type of centrifugal pump used for draining solid particles and long fibers. The inline sewage pump is usually vertical, single-stage, single-suction with the motor close-coupled to the pump head. The suction inlet and discharge outlets are oriented straight to the piping system. The pump combines the characteristic of the basic inline water pump such as a compact structure and inlet and outlet flanges that are cast as a single body. The inline sewage pump’s working operation is based on the principle of gravity-fed sewage directly from the entry point. It uses a unique impeller structure and mechanical seals to effectively contain fibers and solids as they are being transferred. Inline sewage pump is used for transporting sewage, industrial wastewater, and washing industrial mines Inline sewage pumps are widely preferred because of their robust design, portability, and less floor space requirement. However, it requires vertical clearance for installation and can be difficult to maintain.